Interpolation method and interpolation circuit

ABSTRACT

An interpolation method and an interpolation circuit are provided. The interpolation method calculates a difference between values of a first point and a second point and calculates an absolute value of the difference. Then, the absolute value of the difference is used to mix a first function and a second function to obtain a transformation function, which is then used to calculate an interpolation value of an interpolation point between the first point and the second point. Accordingly, the present invention may obtain a result close to high order interpolation without increasing hardware expense.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 98112358, filed on Apr. 14, 2009. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an interpolation method and aninterpolation circuit, and more particularly, to a method and a circuitfor mixing a linear function and a sinusoidal function to performinterpolation.

2. Description of Related Art

Along with the high development of video image technique, digitalcameras and digital camcorders have become one of the indispensabletools in the daily life. These devices may be built with various imageprocessing functions or provide corresponding image processing software,so as to enable a user to magnify the image when taking the image, orbrowse or process the image after taking the image.

When the user needs to take a magnified image of a person or an object,he/she may use the built-in digital zoom function of the device tomagnify the image and then take the shot. When the user needs to browsethe detail of the captured image after taking the shot, he/she may usean image magnifying function of the image processing software associatedwith or accompanied by the camera, so as to get a clearer image.

However, when using the digital cameras in the market to perform adigital zoom in function, edges with sawtooth are often occurred.Similar image distortion may also occur when using image processingsoftware to perform the image zoom in processing. That is because alinear interpolation method or a nearest point interpolation method isused for calculating the interpolation values between each two pixels inan original image and using the same as pixel values of newly addedpixels after the image is magnified when performing the image zoom inprocess.

For example, FIG. 1 is a schematic diagram illustrating a conventionallinear interpolation method of two points. Referring to FIG. 1, A and Bare two adjacent pixels in the original image and are located incoordinates of 0 and 1, respectively. Y is the point to be interpolatedfor, which is located between coordinates 0 and 1 and has a distance xfrom the coordinate 0, wherein 0≦x<1. The interpolation value Y can beobtained through an interpolation formula as shown below:Y=(1−x)×A+x×B  (1)

However, although the calculation of the conventional linearinterpolation method is simpler and the required hardware cost is lower,the calculated image qualify is worse, especially for the high frequencyportion of the image. The image quality is usually unacceptable by theuser. On the other hand, to use a higher order interpolation method tocalculate the interpolation values, pixel values of more pixels arerequired to be referenced. Meanwhile, the size of disposition for theliner buffer should be increased so as to store pixel values of morehorizontal lines. As a result, the cost of the hardware is increased.

SUMMARY OF THE INVENTION

The present invention provides an interpolation method, in whichoriginal linear interpolation coefficients are mapped to a high ordertransformation function, and used to calculate interpolation values, soas to obtain a result close to high order interpolation.

The present invention provides an interpolation circuit, in which anabsolute value of a difference between two points is used to determine amixing weight of a linear function and a sinusoidal function, so as toobtain a transformation function for calculating interpolation values.

The present invention provides an interpolation method, suitable forcalculating an interpolation value of an interpolation point between twopoints. In the present method, a difference between values of a firstpoint and a second point is calculated first, and then an absolute valueof the difference is calculated. Next, a first function and a secondfunction are mixed to obtain a transformation function according to theabsolute value of the difference. Then, the transformation function isused to calculate an interpolation value of an interpolation pointbetween the first point and the second point.

In one embodiment of the present invention, in the step of mixing thefirst function and the second function to obtain the transformationfunction according to the absolute value of the difference, a mixingweight of the first function and the second function is determinedaccording to the absolute value of the difference, and the firstfunction and the second function are mixed to obtain the transformationfunction by using the mixing weight.

In one embodiment of the present invention, in the step of mixing thefirst function and the second function to obtain the transformationfunction by using the mixing weight, the mixing weight m, the firstfunction ƒ₁(x) and the second function ƒ₂(x) are used to calculate thetransformation function ƒ(x) as:ƒ(x)=(1−m)×ƒ₁(x)+m×ƒ ₂(x)

In one embodiment of the present invention, in the step of mixing thefirst function and the second function to obtain the transformationfunction by using the mixing weight, the absolute value of thedifference is compared with a first threshold and a second threshold.When the absolute value of the difference is smaller than or equal tothe first threshold, the first function is used as the transformationfunction. When the absolute value of the difference is larger than thesecond threshold, the second function is used as the transformationfunction. When the absolute value of the difference is larger than thefirst threshold and smaller than or equal to the second threshold, thefirst function and the second function are mixed to obtain thetransformation function.

In one embodiment of the present invention, in the step of mixing thefirst function and the second function to obtain the transformationfunction according to the absolute value of the difference, a mixingweight of the first function and the second function is determinedaccording to the absolute value of the difference, and the firstfunction and the second function are mixed to obtain the transformationfunction by using the mixing weight.

In one embodiment of the present invention, in the step of calculatingthe interpolation value of the interpolation point between the firstpoint and the second point by using the transformation function, adistance d between the interpolation point and the first point issubstituted into the transformation function ƒ(x) to obtain aninterpolation coefficient ƒ(d) of the interpolation point, and theinterpolation coefficient ƒ(d), a value A of the first point and a valueB of the second point are used to calculate the interpolation value Y ofthe interpolation point.

The present invention provides an interpolation circuit, which comprisesan absolute value calculating unit, a transformation functioncalculating unit, and an interpolation value calculating unit. Theabsolute value calculating is used for calculating an absolute value ofan difference between values of a first point and a second point. Thetransformation function calculating unit is used for mixing a firstfunction and a second function to obtain a transformation functionaccording to the absolute value of the difference calculated by theabsolute value calculating unit. The interpolation value calculatingunit is used for calculating the interpolation value of theinterpolation point between the first point and the second point byusing the transformation function obtained by the transformationfunction calculating unit.

In one embodiment of the present invention, the absolute valuecalculating unit comprises a difference calculating component and anabsolute value calculating component. The difference calculatingcomponent is used for calculating a difference between the values of thefirst point and the second point. The absolute value calculatingcomponent is used for calculating the absolute value of the difference.

In one embodiment of the present invention, the transformation functioncalculating unit comprises a mixing weight calculating component and afunction mixing component. The mixing weight calculating component isused for determining a mixing weight of the first function and thesecond function according to the absolute value of the differencecalculated by the absolute value calculating unit. The function mixingcomponent is used for mixing the first function and the second functionto obtain the transformation function by using the mixing weight.

In one embodiment of the present invention, the function mixingcomponent comprises using the mixing weight m, the first function ƒ₁(x)and the second function ƒ₂(x) to calculate the transformation functionƒ(x) as:ƒ(x)=(1−m)×ƒ₁(x)+m×ƒ ₂(x)

In one embodiment of the present invention, the transformation functioncalculating unit further comprises a comparing component, which is usedfor comparing the absolute value of the difference with a firstthreshold and a second threshold. When the absolute value of thedifference is smaller than or equal to the first threshold, the firstfunction is used as the transformation function; when the absolute valueof the difference is larger than the second threshold, the secondfunction is used as the transformation function; and when the absolutevalue of the difference is larger than the first threshold and smallerthan or equal to the second threshold, the first function and the secondfunction are mixed to obtain the transformation function.

In one embodiment of the present invention, when the absolute value ofthe difference is larger than the first threshold and smaller than orequal to the second threshold, the transformation function calculatingunit comprises using the mixing weight calculating component todetermine a mixing weight of the first function and the second functionaccording to the absolute value of the difference, and using thefunction mixing component to mix the first function and the secondfunction to obtain the transformation function by using the mixingweight.

In one embodiment of the present invention, the interpolation valuecalculating unit comprises an interpolation coefficient calculatingcomponent and an interpolation value calculating component. Theinterpolation coefficient calculating component is used for substitutinga distance d between the interpolation point and the first point intothe transformation function ƒ(x) to obtain an interpolation coefficientƒ(d) of the interpolation point. The interpolation value calculatingcomponent is used for calculating the interpolation value Y of theinterpolation point by using the interpolation coefficient ƒ(d), a valueA of the first point, and a value B of the second point.

In one embodiment of the present invention, the first point and thesecond point are pixels having corresponding location in adjacent twohorizontal lines of an image, and the values of the first point and thesecond point are pixel values of the pixels.

In one embodiment of the present invention, the first function and thesecond function comprises a linear function and a sinusoidal function,or a combination thereof.

Based on the above, the interpolation method and the interpolationcircuit of the present invention determines a weight to mix twofunctions according to the absolute value of the difference between twopoints and calculates the transformation function according to theweight. The original linear interpolation coefficient is then mapped tothe transformation function and used to calculate the interpolationvalue between the two points, so as to obtain a result close to highorder interpolation.

In order to make the aforementioned and other features and advantages ofthe present invention more comprehensible, several embodimentsaccompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic diagram illustrating a conventional linearinterpolation method of two points.

FIG. 2 is a flowchart illustrating an interpolation method according toan embodiment of the present invention.

For example, FIG. 3 is an example of calculating a transformationfunction by using a mixing weight.

FIG. 4 is a flowchart illustrating an interpolation method according toan embodiment of the present invention.

FIG. 5 is an example of determining a mixing weight according to theabsolute value of the difference.

FIG. 6 is an example of calculating an interpolation value by using atransformation function.

FIG. 7 is a block diagram of the interpolation circuit according to oneembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention determines a mixing weight of a linear functionand a sinusoidal function according to an absolute value of a differencebetween two points, adjusts an original linear interpolation coefficientthrough the transformation function, and uses the adjusted linearinterpolation coefficient to calculate an interpolation value, such thatthe present invention can achieve a result close to high orderinterpolation with limited hardware expense. Embodiments are given belowfor further illustrating detail steps of the interpolation method andfunctions of the interpolation circuit of the present invention.

FIG. 2 is a flowchart illustrating an interpolation method according toan embodiment of the present invention. Referring to FIG. 2, the presentembodiment is suitable for calculating an interpolation value of aninterpolation point between two points. Wherein, the present embodimentmodifies the original interpolation formula (1) as:Y=(1−ƒ(x))×A+ƒ(x)×B  (2)

Wherein, A and B respectively represent pixel values of adjacent twopixels and Y represents the interpolation value of the interpolationpoint between these two pixels. To compare formula (1) with formula (2),the present embodiment substitutes a ratio x in the originalinterpolation formula (1) into a function ƒ(x). If a higher orderfunction is used to be the function ƒ(x), then the interpolation value Ycalculated by using the function ƒ(x) will be close to a result of highorder interpolation.

It should be noted herein that the foregoing function ƒ(x) is obtainedby mixing two functions with a specific weight, which is determinedaccording to an absolute value of the difference between input twopoints. Accordingly, the interpolation method of the present embodimentcalculates a difference between the values of adjacent first point andsecond point in the image and then calculates an absolute value of thedifference (step S210).

Wherein, said first point and second point are, for example, pixelshaving corresponding location in adjacent two horizontal lines of theimage, or adjacent pixels in same horizontal line of the image. That isto say, the first point and second point are adjacent pixels in avertical direction or in a horizontal direction. In addition, the valuesof the first point and the second point are pixel values of thesepixels.

After the absolute value of the difference is obtained, a first functionand a second function are mixed to obtain a transformation functionaccording to the absolute value of the difference (step S220). Indetail, the present embodiment, for example, determines a mixing weightof the first function and the second function according to the absolutevalue of the difference first, and then uses the same to mix the firstfunction and the second function, so as to obtain the transformationfunction. Wherein, the first function and the second function are, forexample, a linear function, a sinusoidal function, or a combinationthereof, which is not limited by the present embodiment.

For example, FIG. 3 is an example of calculating a transformationfunction by using a mixing weight. Referring to FIG. 3, the presentembodiment assumes the mixing weight is m, a first function is ƒ₁(x)=x,a second function is ƒ₂(x)=(1+sin(π(x−½)))/2, and the calculationformula of the transformation function ƒ(x) is:ƒ(x)=(1−m)×ƒ₁(x)+m×ƒ ₂(x)  (3)

Wherein, the mixing weight m is determined according to an absolutevalue of the difference between the input two points.

After the transformation function is determined, the transformationfunction can be used to calculate an interpolation value of aninterpolation point between the first point and the second point (stepS230). In detail, by substituting a distance d between the interpolationpoint and the first point into the transformation function ƒ(x), aninterpolation coefficient ƒ(d) of the interpolation point is obtained.Then, by substituting the interpolation coefficient ƒ(d) into formula(2), the interpolation value of the interpolation point between thefirst point and the second point can be obtained as:Y=(1−ƒ(d))×A+ƒ(d)×B  (4)

Wherein, A and B respectively represent pixel values of adjacent twopixels and Y represents the interpolation value of the interpolationpoint between these two pixels.

From the above, the method of the present embodiment can determine thetransformation function only according to the absolute value of thedifference between two points. If the transformation function is used tosubstitute for the original linear interpolation coefficient, then aresult close to high order interpolation can be obtained. Therefore, thepresent embodiment may provide better interpolation result withoutincreasing hardware expense.

It should be noted herein that beside the method of mixing two functionswith the specific ratio, the present invention also divides themagnitude of the absolute value of the difference into three intervals,and uses different means to calculate the transformation function ineach of the three intervals. Accordingly, the complexity ofinterpolation calculation can be simplified. An embodiment is givenbelow for further illustration.

FIG. 4 is a flowchart illustrating an interpolation method according toan embodiment of the present invention. Referring to FIG. 4, the presentembodiment is suitable for calculating an interpolation value of aninterpolation point between two points. The steps thereof are asfollows.

First, a difference between the values of adjacent first point andsecond point in an image is calculated and an absolute value of thedifference is further calculated (step S410). Wherein, said first pointand second point are, for example, pixels having corresponding locationin adjacent two horizontal lines of the image, or adjacent pixels insame horizontal line of the image, and the values of the first point andsecond point are pixel values of these pixels.

Next, a first function and a second function are mixed to obtain atransformation function according to the calculated absolute value ofthe difference. The interpolation method of the present embodimentcompares the absolute value of the difference with a first threshold anda second threshold, so as to obtain a transformation function (stepS420). Wherein, when the absolute value of the difference is smallerthan or equal to the first threshold, then the first function is used asthe transformation function (step S430); when the absolute value of thedifference is larger than the second threshold, then the second functionis used as the transformation function (step S440); and when theabsolute value of the difference is larger than the first threshold andsmaller than or equal to the second threshold, the first function andthe second function are mixed according to the absolute value of thedifference so as to obtain the transformation function (step S450). Thefirst function is, for example, a linear function, and the secondfunction is, for example, a sinusoidal function.

In detail, when the absolute value of the difference is relativelysmall, that is, the value of the first point is close to that of thesecond point, it is meaningless to use a high order function tocalculate the interpolation value, such that the present embodimentskips the step of mixing functions and directly uses the linear functionas the transformation function, so as to simplify the calculation; onthe contrary, when the absolute value of the difference is relativelylarge, that is, the value of the first point is far from that of thesecond point, it is meaningless to use the linear function to calculatethe interpolation value, such that the present embodiment also skips thestep of mixing functions and directly uses the sinusoidal function asthe transformation function; however, when the absolute value of thedifference is between the foregoing two situations, the presentembodiment uses the foregoing method of mixing the linear function andthe sinusoidal function to obtain the transformation function, so as toprovide a result close to high order interpolation without increasinghardware expense.

For example, FIG. 5 is an example of determining a mixing weightaccording to the absolute value of the difference. Referring to FIG. 5,a transverse axis represents the absolute value of the difference |A−B|,a vertical axis represents the mixing weight m, and th1 and th2respectively represent the first threshold and the second threshold.

When the absolute value of the difference |A−B| is smaller than thefirst threshold th1, the mixing weight m is equal to 0. To substitutethe mixing weight m into formula (3), a transformation function ƒ(x) canbe obtained as ƒ₁(x).

When the absolute value of the difference |A−B| is larger than the firstthreshold th1 and smaller than or equal to the second threshold th2,then the mixing weight m is used to mix the first function ƒ₁(x) and thesecond function ƒ₂(x) to obtain the transformation function as:ƒ(x)=(1−m)×ƒ₁(x)+m×ƒ ₂(x)

When the absolute value of the difference |A−B| is smaller than thefirst threshold th1, the mixing weight m is equal to 1. To substitutethe mixing weight m into formula (3), a transformation function can beobtained as:ƒ(x)=ƒ₂(x)

After the transformation function is determined, it can be used tocalculate an interpolation value of an interpolation point between thefirst point and the second point (step S460). In detail, by substitutinga distance d between the interpolation point and the first point intothe transformation function ƒ(x), an interpolation coefficient ƒ(d) ofthe interpolation point can be obtained. Then, by substituting theinterpolation coefficient ƒ(d) into formula (2), the interpolation valueof the interpolation point between the first point and the second pointcan be obtained.

For example, FIG. 6 is an example of calculating an interpolation valueby using a transformation function. Referring to FIG. 6, the presentembodiment is a result of the interpolation value calculated by usingthe transformation function of FIG. 5, in which the transverse axisrepresents coordinates of the interpolation point and the vertical axisrepresents the interpolation value of the interpolation point.

When the interpolation point is between the coordinates 0 and 1, due tothe absolute value of the difference being smaller than th1, theinterpolation coefficient x is not adjusted through the transformationfunction ƒ(x) and the method of linear interpolation still remains, suchthat the calculated curve of the interpolation value has a linear form.

When the interpolation point is between the coordinates 1 and 2, due tothe absolute value of the difference being larger than th1 but smallerthan or equal to th2, the transformation function ƒ(x) is adjusted to bebetween the first function ƒ₁(x) and the second function ƒ₂(x), suchthat the calculated curve of the interpolation value has a sinusoidalform.

When the interpolation point is between the coordinates 2 and 3, due tothe absolute value of the difference being larger than th2, thetransformation function ƒ(x) is adjusted to be the sinusoidal functionƒ₂(x), such that the calculated curve of the interpolation value has asinusoidal form.

From the above, the method of the present embodiment determines to usethe linear function, the sinusoidal function, or a combination thereofto be the transformation function according to the variation of thepixel values of adjacent two points, and uses the transformationfunction to substitute for the original linear interpolationcoefficient. Therefore, the complexity of calculation can be simplifiedand a better interpolation result can be obtained.

In accordance with the foregoing interpolation method, the presentinvention also provided a corresponding interpolation circuit, so as torealize each step of the aforesaid interpolation method. An embodimentis given below for further illustration.

FIG. 7 is a block diagram of the interpolation circuit according to oneembodiment of the present invention. Referring to FIG. 7, theinterpolation circuit 700 of the present embodiment comprises anabsolute value calculating unit 710, a transformation functioncalculating unit 720, and an interpolation value calculating unit 730,and the functions thereof are described respectively in the following.

The absolute value calculating unit 710 is used for calculating anabsolute value of a difference between values of adjacent first pointand second point. The absolute value calculating unit 710, for example,uses a difference calculating component 712 to calculate the differencebetween the values of the first point and the second point and then usesan absolute value calculating component 714 to calculate the absolutevalue of the difference. Wherein, said first point and second point are,for example, pixels having corresponding location in adjacent twohorizontal lines of the image, or adjacent pixels in same horizontalline of the image, and the values of the first point and second pointare pixel values of these pixels.

The transformation function calculating unit 720 is used for mixing afirst function and a second function to obtain a transformation functionaccording to the absolute value of the difference calculated by theabsolute value calculating unit 710. The transformation functioncalculating unit 720, for example, uses a mixing weight calculatingcomponent 722 to determine a mixing weight of the first function and thesecond function according to the absolute value of the differencecalculated by the absolute value calculating unit 710 and uses functionmixing component 724 to mix the first function and the second functionto obtain the transformation function by using the mixing weight.Wherein, the method for calculating the transformation function has beendescribed in the foregoing embodiment, so the related content is omittedherein.

It should be noted herein that the transformation function calculatingunit 720 further comprises a comparing component 726, which is used forcomparing the absolute value of the difference with a first thresholdand a second threshold. Wherein, when the comparing component 726determines that the absolute value of the difference is smaller than orequal to the first threshold, then transformation function calculatingunit 720 uses the first function as the transformation function (stepS430); when the comparing component 726 determines that the absolutevalue of the difference is larger than the second threshold, thentransformation function calculating unit 720 uses the second function asthe transformation function (step S440); and when the comparingcomponent 726 determines that the absolute value of the difference islarger than the first threshold and smaller than or equal to the secondthreshold, then the transformation function calculating unit 720 mixesthe first function and the second function to obtain the transformationfunction according to the absolute value of the difference.

The interpolation value calculating unit 730 uses the transformationfunction calculated by the transformation function calculating unit 720to calculate an interpolation value of an interpolation point betweenthe first point and the second point. In detail, the interpolation valuecalculating unit 730 uses an interpolation coefficient calculatingcomponent 732 to substitute a distance d between the interpolation pointand the first point into the transformation function ƒ(x), so as toobtain the interpolation coefficient ƒ(d) of the interpolation point.Next, the interpolation value calculating unit 730 uses an interpolationvalue calculating component 734 to calculate the interpolation value Yof the interpolation point according to the interpolation coefficientƒ(d), a value A of the first point, and a value B of the second point.Wherein, the method for calculating the interpolation value has beendescribed in the foregoing embodiment, so the related content is omittedherein.

In summary, when an image processing device or software performs animage magnifying function, it can store the horizontal lines of theimage into a line buffer, so as to execute interpolation valuecalculation between each two pixels. Wherein, for the interpolationvalue in a horizontal direction, the device may calculate throughinterpolation of pixels in the same horizontal line, but for theinterpolation value in a vertical direction, the device has to calculatethrough interpolation of corresponding pixels in adjacent horizontallines. However, through the interpolation method and the interpolationcircuit of the present invention, only pixel values of a current pixeland a corresponding pixel in a previous horizontal line are referenced,and then the interpolation coefficient can be adjusted by the absolutevalue of the difference between the two pixels. Therefore, the presentinvention can achieve a result close to high order interpolation byusing only one line buffer.

Although the present invention has been described with reference to theabove embodiments, it will be apparent to one of the ordinary skill inthe art that modifications to the described embodiment may be madewithout departing from the spirit of the invention. Accordingly, thescope of the invention will be defined by the attached claims not by theabove detailed descriptions.

What is claimed is:
 1. An interpolation method, suitable for calculatingan interpolation value of an interpolation point between two points ofan image, the interpolation method performed by a processor of an imageprocessing device comprising: calculating a difference between pixelvalues of a first point and a second point of the image by theprocessor; determining a mixing weight of a first function and a secondfunction according to an absolute value of the difference by theprocessor; mixing a first function and a second function according tothe mixing weight to obtain a transformation function ƒ(x) by theprocessor; substituting a distance d between the interpolation point andthe first point into the transformation function ƒ(x) to obtain aninterpolation coefficient ƒ(d) of the interpolation point by theprocessor; and calculating the interpolation value of the interpolationpoint between the first point and the second point by using theinterpolation coefficient ƒ(d) and the pixel values of the first pointand the second point by the processor.
 2. The interpolation methodaccording to claim 1, wherein the step of mixing the first function andthe second function by using the mixing weight to obtain thetransformation function comprises: using the mixing weight m, the firstfunction ƒ₁(x), and the second function ƒ₂(x) to calculate thetransformation function ƒ(x) as:ƒ(x)=(1−m)×f ₁(x)+m×f ₂(x).
 3. The interpolation method according toclaim 1, wherein determining the mixing weight of the first function andthe second function and mixing the first function and the secondfunction by using the mixing weight to obtain the transformationfunction comprises: comparing the absolute value of the difference witha first threshold and a second threshold; using the first function asthe transformation function when the absolute value of the difference issmaller than or equal to the first threshold; using the second functionas the transformation function when the absolute value of the differenceis larger than the second threshold; and mixing the first function andthe second function to obtain the transformation function when theabsolute value of the difference is larger than the first threshold andsmaller than or equal to the second threshold.
 4. The interpolationmethod according to claim 1, wherein the first point and the secondpoint are pixels having corresponding location in adjacent twohorizontal lines of the image.
 5. The interpolation method according toclaim 1, wherein the first function and the second function comprises alinear function and a sinusoidal function, or a combination thereof. 6.An interpolation circuit in an image processing device, theinterpolation circuit comprising: an absolute value calculatingcircuitry, for calculating an absolute value of an difference betweenpixel values of a first point and a second point of an image; atransformation function calculating circuitry, for determining a mixingweight of a first function and a second function according to theabsolute value of the difference calculated by the absolute valuecalculating circuitry and for mixing a first function and a secondfunction ƒ(x) according to the mixing weight to obtain a transformationfunction; and an interpolation value calculating circuitry, forsubstituting a distance d between the interpolation point and the firstpoint into the transformation function ƒ(x) to obtain an interpolationcoefficient ƒ(d) of the interpolation point and for further calculatingan interpolation value of an interpolation point between the first pointand the second point by using the interpolation coefficient ƒ(d) and thepixel values of the first point and the second point.
 7. Theinterpolation circuit according to claim 6, wherein the absolute valuecalculating circuitry comprises: a difference calculating component, forcalculating the difference between the values of the first point and thesecond point; and an absolute value calculating component, forcalculating the absolute value of the difference.
 8. The interpolationcircuit according to claim 6, wherein the transformation functioncalculating circuitry comprises: a mixing weight calculating component,for determining the mixing weight of the first function and the secondfunction according to the absolute value of the difference calculated bythe absolute value calculating circuitry; and a function mixingcomponent, for mixing the first function and the second function toobtain the transformation function by using the mixing weight.
 9. Theinterpolation circuit according to claim 8, wherein the function mixingcomponent comprises using the mixing weight m, the first function ƒ₁(x),and the second function ƒ₂(x) to calculate the transformation functionƒ(x) as:ƒ(x)=(1−m)×f ₁(x)+m×f ₂(x).
 10. The interpolation circuit according toclaim 8, wherein the transformation function calculating circuitryfurther comprises: a comparing component, for comparing the absolutevalue of the difference with a first threshold and a second threshold,wherein when the absolute value of the difference is smaller than orequal to the first threshold, the first function is used as thetransformation function; when the absolute value of the difference islarger than the second threshold, the second function is used as thetransformation function; and when the absolute value of the differenceis larger than the first threshold and smaller than or equal to thesecond threshold, the first function and the second function are mixedto obtain the transformation function.
 11. The interpolation circuitaccording to claim 10, wherein when the absolute value of the differenceis larger than the first threshold and smaller than or equal to thesecond threshold, the transformation function calculating circuitrycomprises using the mixing weight calculating component to determine themixing weight of the first function and the second function according tothe absolute value of the difference, and using the function mixingcomponent to mix the first function and the second function to obtainthe transformation function by using the mixing weight.
 12. Theinterpolation circuit according to claim 6, wherein the interpolationvalue calculating circuitry comprises: an interpolation coefficientcalculating component, for substituting the distance d between theinterpolation point and the first point into the transformation functionƒ(x) to obtain the interpolation coefficient ƒ(d) of the interpolationpoint; and an interpolation value calculating component, for calculatingthe interpolation value Y of the interpolation point by using theinterpolation coefficient ƒ(d), the pixel value A of the first point,and the pixel value B of the second point.
 13. The interpolation circuitaccording to claim 6, wherein the first point and the second point arepixels having corresponding location in adjacent two horizontal lines ofan image, and the pixel values of the first point and the second pointare pixel values of the pixels.
 14. The interpolation circuit accordingto claim 6, wherein the first function and the second function comprisesa linear function and a sinusoidal function, or a combination thereof.